1. Field of the Invention
The present invention relates to a high-speed rotation testing apparatus, and in particular, to a high-speed rotation testing apparatus preferably used to check the performance and strength of a rotating member of a mechanical element of an apparatus for airplane engines, heavy electrical equipment, grinding stones, generators, ships, automobiles, etc.
2. Description of the Related Art
Conventional high-speed testing apparatuses will be described. The high-speed rotation testing apparatus generally tests industrial products (for example, fans and other rotating members) that are rotated during operation. The high-speed rotation testing apparatus rotates a test object at a rotation speed rated for the operation of the test object to test the reliability thereof under these conditions.
Further, in addition to the check on the rated rotation of the test object prior to incorporation into the actual machine described above (such as an airplane engine), the high-speed rotation testing apparatus is used for various other applications depending on its object, including checks on the safety during overspeed, checks on the rupture strength exhibited when centrifugal stress is forcibly applied, checks on the fatigue strength exhibited when the rotation speed is alternately increased and reduced for a long time (cycle test), tests in which the test object is permanently distorted, and tests in which a distortion gauge is stuck to the test object to measure the stress and distortion during rotation. Accordingly, this apparatus is essential in the industrial fields that use high-speed rotating parts. Recent high-speed rotation testing apparatuses mainly use two types of drive sources for rotation: one of these types uses an air turbine, and the other is based on a gear speed-increase motor driving method that uses a driving motor.
FIG. 5 shows a part of a high-speed rotation testing apparatus based on the air turbine method. The high-speed rotation testing apparatus 100 comprises an air turbine 102 that is rotated by receiving compressed air from a compressor 101, a support shaft 103 holding a test object S and is rotated by receiving torque applied by the air turbine 102, a storage section 105 that stores the test object S, supported by the support shaft 103, and a damper 107 for the support shaft 103. The test object S is an object shaped like a rotating member which has its durability under high-speed rotation tested as described previously.
The air turbine 102 comprises a casing 104 rotatably storing and supporting a rotor 106. Compressed air from the air compressor 101 blows against a bucket portion of the rotor 106 to apply a rotational force to the rotor 106. Thus, the rotor 106 outputs torque.
On the other hand, the casing 104 and the storage section 105 are integrated together. The casing 104 supports the rotor 106 so that when the casing 104 and the storage section 105, integrated together, are placed on a horizontal surface, the rotational center line of the rotor 106 is arranged toward the vertical direction of the apparatus. Further, the rotor 106 is concentrically fixed (connected) to the support shaft 103.
Furthermore, the test object S is held at the lower end of the support shaft 103. The support shaft 103 has a holding mechanism (not shown) provided at the lower end thereof. The holding mechanism fixes the rotating-member-shaped test object S concentrically to a rotating shaft at the rotational center of the test object S by, for example, bolting or screwing. Thus, the test object S rotates with the support shaft 103.
With this construction, when the compressor 101 is activated, the support shaft 103 and the test object S are rotated with the rotor 106. Then, the flow of compressed air from the compressor 101 is controlled so that the rotation speed of the test object S has the target value. Then, high-speed rotation tests are carried out for a predetermined time.
FIG. 6 shows a part of a high-speed rotation testing apparatus 200 using a driving motor as a drive source. The high-speed rotation testing apparatus 200 comprises a driving motor 201, a gear train 202 rotated by the driving motor 201, a support shaft 203 holding the test object S and is rotated by receiving torque from the gear train 202, a casing 204 for supporting the driving motor 201, the gear train 202, and the support shaft 203, a storage section 205 that stores the test object S supported by the support shaft 203, and a damper 210 for the support shaft 203.
The casing 204 and the storage section 205 are integrated together. The casing 204 supports the driving motor 201 so that when the casing 204 and the storage section 205, integrated together, are placed on a horizontal surface, a rotor shaft 201a of the driving motor 201 is arranged toward the vertical direction of the apparatus. The gear train 202 comprises a driving gear 206 and a driven gear 207 driven thereby. A support shaft 206a of the driving gear 206 is connected to the rotor shaft 201a, and a support shaft 207a of the driven gear 207 is fixedly and concentrically connected to the support shaft 203. The casing 204 supports the support shafts 206a, 207a, and 203 so that these shafts are arranged toward the vertical direction. The gear train 202 also serves to increase a rotation speed transmitted from the driving motor 201 to the support shaft 203. In the high-speed rotation testing apparatus 200 shown in FIG. 6, the gear train 202 is illustrated to be composed only of spur gears but may be composed of other various gears such as planetary, helical, and bevel gears. Alternatively, instead of the gear train, a belt may be used to transmit torque and increase the rotation speed.
Furthermore, the test object S is fixed at the lower end of the support shaft 203 via the above described support shaft 103 and a holding mechanism (not shown). Thus, the test object S rotates with the support shaft 203.
With this construction, when the driving motor 201 is rotated, the support shaft 203 and the test object S are rotated by the gear train 202. Then, the driving motor 201 is controlled so that the rotation speed of the test object S, achieved via the gear train 202, has the target value. In this manner, high-speed rotation tests are conducted as in the case with the high-speed rotation testing apparatus 100.
Long-time cyclic operation (the rotation speed of the rotating member is alternately set for an upper and a lower limit values) intended to check the fatigue strength of a rotating member represented by an airplane engine has recently frequently been performed in every field, for example, in the fields of research and trial production and product shipment. To such long-time tests, it is important to reduce tests costs and improve the maintainability of the testing apparatus.
The above described high-speed rotation testing apparatus 100 using the air turbine 102 allows easy maintenance owing to the simplified structure of the air turbine. Further, the high-speed rotation testing apparatus 100 must use the compressor 101 because compressed air is required to drive the air turbine. In this case, the rotor of the air turbine rotates using air as a medium, so that energy is prone to be lost when compressed air blows against the rotor to apply rotational force to the rotor. Accordingly, the air compressor 101 must provide about 37-kW power even for small-sized high-speed rotation testing apparatuses and 300-kW or more power for large-sized high-speed rotation testing apparatuses. Consequently, the high-speed rotation testing apparatus 100 disadvantageously consumes a huge amount of power for the above described tests requiring a long-time continuous operation. Further, since the compressor 101 generates heat, it is disadvantageously difficult to operate the high-speed rotation testing apparatus for a long time. Furthermore, although the high-speed rotation testing apparatus 100 controls the rotation speed of the test object S by controlling the flow of compressed air from the air compressor 101, it is difficult to precisely control the rotation speed of the test object S because air is used as a medium for applying torque to the rotor 106. Therefore, also owing to the difficulties with which the rotation speed of the test object S is controlled, the conventional high-speed rotation testing apparatus 100 is unsuitable for high-speed rotation tests that must be conducted for a long time.
On the other hand, the high-speed rotation testing apparatus 200 based on the gear speed-increase motor driving method and which uses the driving motor 201 as a drive source has the following disadvantages: The driving motor 201 comprises a rotor 208 and a stator 209, and the clearance between the rotor 208 and the stator 209 significantly affects output from the driving motor 201. That is, the rotor 208 vibrates in the direction of the rotational radius of the apparatus, and this vibration leads to an energy loss. Accordingly, it is necessary to reduce the vibration in the direction of the rotational radius, which occurs in the rotor 208. In the above described high-speed rotation tests in which the test object S is rotated at high speed or the rotation speed of the test object S is varied, the vibration in the direction of the rotational radius may occur notably in the support shaft 103. Therefore, the high-speed rotation testing apparatus 200 requires the gear train 202 to be interposed between the rotor shaft 201a and the support shaft 203.
However, when the gear train 202 is interposed between the driving motor 201 and the support shaft 203, the number of required parts such as gears, support shafts, and bearings therefor increases. Thus, disadvantageously, the structure of the high-speed rotation testing apparatus becomes complicated, and the maintenance of the apparatus thus becomes difficult. Further, in the high-speed rotation testing apparatus 200 with the gear train 202 interposed between the driving motor 201 and the support shaft 203, mechanical losses may result from the engagement between the gear 206 and 207 and from the friction between the support shafts 206a and 207a and the bearings therefor. This hinders output from the driving motor 201 from being efficiently transmitted to the test object, thereby preventing the full use of the output. Further, adjustment of the rotation speed of the test object S may result in a variation in this rotation speed. Furthermore, because of the use of the gear train 202, noise may occur from the gear 206 or 207, or the gear train 202 itself may vibrate to adversely affect the test object S.
The above described mechanical losses may amount to at least about 20 to 30% of the output from the driving motor 201 and even to about 50% thereof, depending on the structure of the apparatus. Consequently, the duration per cycle of the above-described cyclic tests or the like increases during which the rotation speed is increased and reduced by, for example, setting an upper and a lower limit value therefor. As a result, the tests disadvantageously require a very long time. Further, it should be appreciated that the mechanical losses increase the power consumption of the driving motor and that the power consumption further increases owing to the extended duration of the tests.
As described above, although the high-speed rotation tests are frequently used for research and development and for products, the conventional high-speed rotation testing apparatus has the above described disadvantages, which hinder progress in the development of products requiring high-speed rotation.
It is an object of the present invention to provide a high-speed rotation testing apparatus that improves the disadvantages of the conventional examples and in particular improves maintainability, reduces tests costs, and has a simplified structure.
The present invention provides a high-speed rotation testing apparatus for rotating a test object to check strength and durability thereof under the rotation, the apparatus comprising a spindle holding the test object at a lower end thereof, a driving motor for applying torque to the spindle, and a frame for supporting a rotor shaft of the driving motor so that the rotor shaft is arranged toward a vertical direction.
The spindle is inserted into a through-hole formed in a center of the rotor shaft, and an upper end of the rotor shaft and an upper end of the spindle are fixed together, thereby allowing the spindle to be driven directly by the driving motor. The through-hole having an inner diameter for allowing a clearance in which the lower end of the spindle can swing, and a damping mechanism for restricting the pivoting is arranged close to the lower end of the spindle projecting from the lower end of the rotor shaft.
In the present invention, the xe2x80x9cframe for supporting the rotor shaft so that the rotor shaft is arranged toward a vertical directionxe2x80x9d means that when the frame is ready for high-speed rotation tests (for example, it is installed on a horizontal surface), it supports the rotor shaft so that the shaft is arranged toward the vertical direction.
With the above configuration, the spindle holding the test object is installed in the through-hole formed in the rotor shaft of the driving motor. Thus, no gear train is interposed between the rotor shaft and the spindle as in the conventional high-speed rotation testing apparatus. This prevents the degradation of maintainability and mechanical losses which are caused by an increase in the number of parts associated with the provision of the gear train.
The rotor shaft and the spindle are connected together only at the upper ends thereof. Further, the damping mechanism is arranged in the vicinity of the lower end of the spindle to restrict it from vibrating. Furthermore, the clearance is formed between the spindle and the through-hole at the location corresponding to the middle of the spindle. Without any clearance between the spindle and the through-hole in the rotor shaft, if the center of gravity of the test object is offset from the center line of the spindle, that part of the spindle which projects from the lower end of the rotor shaft may be deflected in the direction of the rotational radius of the apparatus, causing the spindle to be broken down. Further, vibration caused by the deflection of the spindle is transmitted directly to the rotor of the driving motor, resulting in a failure or defect in the driving motor.
However, in the present invention, the clearance between the through-hole and the spindle allows the entire spindle to swing around the upper end thereof. This avoids concentrating stress on the part of the spindle which projects from the lower end of the rotor shaft.
Furthermore, the spindle is damped by the damping mechanism in the vicinity of the test object, which may cause vibration. Accordingly, even if that part of the spindle on which the test object is held, that is, the vicinity of the test object, is vibrated in the direction of the rotational radius occurs in, energy obtained by swing spindle is transmitted to the frame.
Further, the spindle is fixed to the rotor shaft at the upper end thereof which is located remote from the test object. Thus, even if that part of the spindle on which the test object is held is vibrated in the direction of the rotational radius, this vibration is converted into swing around the upper end of the spindle. Thus, the vibration occurring at the upper end of the spindle has only a small displacement and is thus sufficiently restrained from being transmitted from the upper end of the spindle to the upper end of the rotor shaft.
Therefore, according to the present invention, high-speed rotation tests can be carried out by efficiently transmitting the torque of the driving motor to the test object, while eliminating the defects of the gear train.
The construction of another high-speed rotation testing apparatus, which is different from the above, will be described below. This high-speed rotation testing apparatus comprises a spindle holding the test object at a lower end thereof, a driving motor for applying torque to the spindle, a weight supporting shaft having a through-hole in a center thereof, the through-hole being penetrated by the spindle, and a frame for supporting a rotor shaft of the driving motor and the weight supporting shaft so that these shafts are arranged toward a vertical direction.
The rotor shaft and the spindle are connected together so that center lines of the rotor shaft and the spindle are aligned with each other, and the spindle extends below a lower end of the rotor shaft. Further, the spindle is inserted into the through-hole in the weight supporting shaft, and an upper end of the weight supporting shaft is connected to the spindle. The frame rotatably supports the weight supporting shaft via a thrust bearing. The through-hole in the weight supporting shaft having an inner diameter for allowing a clearance to be formed in which the lower end of the spindle can swing, and a damping mechanism is arranged for restricting the swing of a vicinity of the lower end of the spindle projecting from the lower end of the weight supporting shaft.
In this high-speed rotation testing apparatus, which is different from the high-speed rotation testing apparatus described previously, the spindle is inserted into the weight supporting shaft below the rotor shaft, the weight supporting shaft comprising the through-hole providing the clearance. Then, the upper end of the weight supporting shaft is connected to the spindle, and the damping mechanism damps the spindle below the weight supporting shaft.
With this construction, the spindle may vibrate around the junction between the spindle and the upper end of the weight supporting shaft, but this vibration is restrained by the damping mechanism. Accordingly, during swing, the spindle may be bent between the junction between the spindle and the weight supporting shaft and the lower end of the spindle. Furthermore, the swing of the spindle is restricted by the damping mechanism, thereby avoiding the breakdown of the spindle resulting from stress concentration as in the case with the previously shown high-speed rotation testing apparatus. Since the upper end of the weight supporting shaft supported by the thrust bearing and the spindle are connected to each other, the swing of the spindle is not transmitted above the junction, thereby influence of the swing of the spindle on the rotor shaft being avoided. Thus, this high-speed rotation testing apparatus have the same advantages as the high-speed rotation testing apparatus initially described.
Furthermore, since the weight supporting shaft supported by the frame and the spindle is connected to each other via a thrust bearing, even if a test subject with large weight is attached to the spindle, the weight load of the subject is applied to the frame through the weight supporting shaft. Accordingly, this high-speed rotation testing apparatus allows a high-speed rotation testing for a test subject with a larger weight than the case of the high-speed rotation testing apparatus initially described.
Further, the above described damping mechanism may have a journal bearing corresponding to the spindle, a housing for supporting the journal bearing, and a storage chamber formed in the frame and which holds the housing so that it can swing with the spindle, the storage chamber being filled with a lubricant.
In this case, the spindle is inserted into the journal bearing with a clearance formed therebetween, and the lubricant flows into the clearance. When the spindle rotates at high speed, the lubricant serves to exert film pressure against the spindle to guide the journal bearing so that the spindle is located at the center of the journal bearing. At this time, the spindle is subjected to resistance from the lubricant flowing through the clearance in the journal bearing. Furthermore, as the spindle swings, the journal bearing swings responsively. However, the lubricant is already present between the journal bearing and the housing, so that when the journal bearing swings relative to the housing, it undergoes flow resistance from the lubricant.
On the other hand, the housing, supporting the journal bearing, is subjected to reaction from the journal bearing via the lubricant and guided in the same direction as that in which the spindle is guided. Accordingly, when the spindle is vibrated in the direction of the rotational radius (swing around the upper end of the spindle), the housing swings similarly to the spindle, but undergoes flow resistance from the lubricant again because it is inside the storage chamber, filled with the lubricant.
That is, during swing, the spindle undergoes all the flow resistance from the lubricant between the spindle and journal bearing, between the journal bearing and the housing, and between the housing and the storage chamber. Consequently, these viscous resistances serve to damp the spindle to restrain it from swing.
Alternatively, the spindle may be extended downward so that a sufficiently long part of the spindle projects from the lower end of the rotor shaft, and the projecting part may be supported by the frame via the thrust bearing. In this case, since the load of the test object is supported by the frame via the thrust bearing, heavier test objects can be subjected to high-speed rotation tests.
Further, the above described construction of the present invention may include a storage container in which the test object held by the spindle is stored to prevent crushed pieces of the test object from scattering. Furthermore, the storage container is desirably a vacuum vessel from which an internal gas can be discharged. The storage container enables high-speed rotation tests to be carried out up to the limits beyond which the test object is broken down. Further, if the storage container is a vacuum vessel, the periphery of the test object can be formed into a vacuum before the tests. Consequently, windage losses are eliminated to enable the rotation speed to be promptly increased up to a target value.
The present invention attains the object described previously, using the above described constructions.